MUSEUM OF COMPARATIVE ZOOLOGY. 99 



contraction from preservation in strong alcohol.] The epimera of the first three 

 somites are large and project backward in an angle, while the epimera of the 

 fourth and fifth somites project backward quite as far, but have the outline more 

 rounded. The sixth somite is about as long as the antennal scale, considerably 

 more than half as high as long, and strongly compressed. 



The telson is considerably shorter than the sixth somite, flattened and 

 slightly sulcated above, with a deep lateral groove each side, acutely angular at 

 the tip, and ciliated along the edges. The inner lamella of the oropod is a little 

 longer than the telson, about three and a half times as long as broad, and lance- 

 olate at the tip. The outer lamella is between a third and a fourth longer than 

 the inner, less than a fourth as broad as long, the cuter margin terminating in 

 a strong tooth about two thirds of the way from the base to the tip, and the 

 tip narrow, but rounded. 



The peculiar sexual appendages (petasma, Fig. 8) of the first somite of the 

 abdomen have essentially the same structure as in S. arcticus, but are much 

 more complicated than would be inferred from the figures for that species given 

 by Kroyer. The appendages of the two sides are usually hooked together along 

 the middle line (h), but are really entirely distinct. Each is attached by a 

 narrow process (a) to the protopod of the abdominal appendage, and is divided 

 by more or less distinct sutures into three portions. The outer portion, that 

 next the protopod, projects above the point of attachment in a narrow process, 

 and below the point of attachment in a broad lamellar lateral expansion, and 

 below this in a long, flat, chitinous stylet (b) terminating in a sharp hook below 

 a rounded sinus in the extremity. The middle portion projects below and 

 alongside of, but far beyond, the hooked stylet (b), in a complicated appendage 

 divided distally into three membranaceous and hook-hearing processes (e,f, g) 

 and bearing two slender and unarmed stylets (c, d) ; and each of the membra- 

 naceous processes is armed along one edge with a series of peculiar chitinous 

 hooks retracted within invaginated papillae (Fig. 8 b ), and at the tip with a 

 larger and somewhat differently shaped but similarly retracted hook (Fig. b"). 

 The lateral honks themselves are semi-mushroom-shaped, like those which serve 

 to hook together the inner rami of the abdominal appendages in many crus- 

 taceans, and very much like those along the mesial edge (/<) of this same 

 appendage, but larger. The terminal hooks are more properly hook-shaped, as 

 shown in the figure, but are broad at the tips. The invagination of the mem- 

 brane around the hooks is possibly due to contraction in the alcoholic speci- 

 mens, but the hooks are similarly retracted in all the specimens of S. arcticus 

 which I have examined, their bases appear to be connected with Btrong mus- 

 cular fibres, and I think there ia little doubt that the honks are capable of 

 being retracted in life. The mesial portion of appendages is thin, lamellar, 

 longitudinally folded, and armed along the mesial edge with great numbers of 

 semi-mushroom-shaped hooks which serve to attach together the appends 

 the two sides. 



The branchieB are the same in number and have the same arrangement as in 

 S. arcticus, but the posterior branchia on the twelfth (antepenultimate) somite 



